Inkjet type printers typically employ a print cartridge that is moved in a transverse fashion across a print medium. A disposable inkjet print cartridge typically includes a self-contained ink container, a printhead supporting a plurality of inkjet nozzles in combination with the ink container, and a plurality of external electrical contacts for connecting the inkjet nozzles to driver circuitry in the printer. Failure of a disposable print cartridge is usually related to the failure of the individual resistors used to heat the ink in proximity to each nozzle. However, as the inkjet technology has advanced, the reliability of the print cartridges has improved dramatically over the past years. Current printhead assemblies used in the disposable inkjet print cartridges are fully operable to their original print quality specifications after printing tens or even hundreds of times the amount of ink contained in the self-contained ink container. It is, therefore, desirable to extend the life of a print cartridge to take advantage of the long life of the printhead assembly. This helps tremendously reduce dumping of waste print cartridges to the landfill to save the environment, in addition to long term running cost. Merely making the print cartridge container larger in size is not a satisfactory solution. The print cartridges are typically mounted on the moving carriage of the inkjet printer. The larger the volume of ink in the print cartridge, the greater the mass is to be moved by the printer carriage. The greater mass places a greater burden on the motor that drives the carriage as well as the structure of the carriage itself. Printer performance will also be limited by a heavier carriage because of the increased inertia associated with a larger carriage. That inertia must be overcome at the two endpoints of the carriage motion. At these locations, the carriage reverses direction to begin another pass over the medium during the printing process. Increased carriage inertia increases the time required to reverse direction for a given driving motor size and, therefore, can reduce print speed.
U.S. Pat. No. 5,686,947 to Murray et al., discloses a wide format inkjet printer that provides a substantially continuous supply of ink to a print cartridge from a large, refillable ink reservoir mounted within the inkjet printer. Flexible tubing, permanently mounted within the inkjet printer, connects the reservoir to the printhead. The off-carriage ink supply allows a print cartridge to potentially print in the printer for the full cartridge life while eliminating the problems related to the extra weight on the carriage of an on-carriage large ink delivery system, resulting in elongated printer life and more importantly significantly reduced waste print cartridges dumped to landfill.
It should be understood, however, that the continuous replenishment of the ink container within a disposable inkjet print cartridge by simply applying the gravity-and-siphon method, such as the one used in U.S. Pat. No. 5,686,947, may bear some undesirable consequences, i.e., an undesirable ink pressure variation at the printhead. When the ink pressure variation at the printhead exceeds certain limit, printhead failure, such as ink burping or nozzle depriming can occur. It therefore becomes important to control ink pressure variation in order to achieve the best image quality. A variety of factors may induce ink pressure variation at the printhead. For example, a change in the ink level in the refillable ink reservoir is directly related to the ink pressure change at the printhead. Also, printer throughput and the carriage motion speed may cause variations of dynamic ink pressure. It has been found that, typically, that the higher the printer throughput, the greater the variation of ink pressure at the printhead. Similarly, the speed at which the carriage travels will affect the dynamic ink pressure range. At the endpoints of the carriage motion, it accelerates to reverse its moving direction. The acceleration causes the ink in the flexible tubing to flow in and out of the print cartridge, therefore, increasing pressure variation at the printhead. It is appreciated to note that the faster the carriage motion, the greater the ink pressure variation at the printhead.
Fluid pressure dampening device, or pulsation dampener, has long been used in the industry of pump and fluids to suppress pressure variation. However, ink jet printing system imposes very special requirements to the ink delivery system design, including very small pressure range, i.e., down to inches of water, and small design size to fit into the printer frame and especially on the moving carriage.
U.S. Pat. No. 4,342,042 by Cruz-Uribe et al. discloses an ink delivery system including a small reservoir having a flexible membrane attached on its upper open side. A similar ink delivery system is taught in U.S. Pat. No. 4,347,524 by Engel et al. The ink delivery system has a shock absorbing device comprising a fluid restriction tube and a compliance reservoir which either is partially filled with air or has a flexible diaphragm wall.
Japanese Kokai Utility Model Application Number 60-120840 and Japanese Patent Number 2748458 by Suzuki from Seiko-Epson Corporation disclose an ink delivery system involves a damper between an ink tank and a printhead. The damper has a chamber formed above the inlet and outlet ports by attaching two pieces flexible damper film to the opposite sides of the damper substrate. The ink pressure variation is absorbed by the compression of air in the chamber and the deflection of the damper film.
Japanese Kokai Patent Application Number 03-205157 by Nagasaki and Japanese Kokai Patent Application Number 03-208665 by Tsuneo, both from Fujitsu Ltd., and U.S. Pat. No. 5,030,973 by Nonoyama et al. assigned to Fujitsu Ltd., disclose a type of damper in an ink delivery system comprising a chamber formed in the substrate between two pieces of flexible film. The damper further includes a filter incorporated in the damper body and a bubble discharge path connected to the top portion of the chamber.
U.S. Pat. No. 6,244,698 by Chino et al. and U.S. Pat. No. 6,460,986 by Sasaki et al., both assigned to Seiko-Epson Corporation, incorporate pressure a damper as part of a printhead unit.
Therefore, there has been long and continuous interest in the ink jet printer industry to improve ink delivery system by incorporating a pressure damping device in order to delivery ink to the printhead with the optimized ink pressure for the best printing performance.